Aircraft automatic pilot turn control



Aug. 10, 1954 P. HALPERT AIRCRAFT AUTOMATIC PILOT TURN coNTRoL 2 Sheets-Sheet l Filed Sept. 10, 1948 NAW@ . INVENTOR PERCY HAL/@ERT Aug. l0, 1954 P. HALPERT AIRCRAFT AUTOMATIC PILOT TURN CONTROL 2 Sheets-Sheet 2 Filed Sept. l0, 1948 QNN /DE/Tcv HALF/SRT Patented Aug. 10, 1954 AIRCRAFT AUTOMATIC PILOT TURN CON TROL Percy Halpert, Hempstead, N.

Y., assigner to The Sperry Corporation, Great Neck, N. Y., a corporation of Delaware Application September 10, 1948, Serial No. 48,669

19 Claims. 1

The present invention relates to automatic pilots for aircraft that are capable oi turning about the vertical axis thereof and approximately retaining a constant or natural rate of turn for a constant banking angle and speed. ln accordance with the invention, the improved automatic pilot functions so that the craft is permitted to assume a natural rate of turn depending on its aerodynamic properties and the turn rate is then coordinated or stabilized at that value. Heretofore, automatic pilots were eifective to cause the craft to enter and continue a banked turn at an arbitrary rate and various ways were employed to maintain the rate of turn of the craft at the established arbitrary rate. As the arbitrary turn rate heretofore established by the automatic pilot very seldom coincided with the natural rate of turn of the craft for the given banking angle and speed, the turns produced were not smooth. The primary object of the present invention is to obviate this condition in the manner heretofore described so that the craft is controlled to provide as smooth a turn as possible.

The term natural rate of turn of the craft as herein employed is dened as the coordinated turn rate associated with a given bank angle and air speed of the craft. it is assumed here that such a rate of turn is brought about by the inherent directional stability of the craft with substantially Zero side slip or skid when the rudder or other azimuth control is centralized in a steady state condition.

With the improved automatic pilot turn control, no adjustment for air speed is required as the system provides coordinated rate stabilized turns at all craft speeds. However, it is desirable that the speed of the craft for a given banked turn be maintained constant.

One of the features of the invention resides in the provision of a turn rate correcting means for the automatic pilot in the form of a followup system with a motor having suiiicient inertia that the time required for the motor to change its speed is longer than the time for the craft to return to its natural rate of turn after it has departed from the same.

A further feature of the present invention is provided by the employment of a signal in acn cordance with the rate of roll of the craft for operating the rudder servomotor of the auto matic piiot during turns of the craft about its vertical axis.

Other objects, features and structural details of the invention will be apparent from the following description when read in connection with the accompanying drawings wherein,

Fig. 1 is a diagrammatic view and circuit diagram of an automatic pilot embodying the present inventive concepts, and

Fig. 2 is a similar view showing a modified form of the invention.

With reference to the drawings, the improved automatic pilot is shown to include an azimuth reference or directional gyro indicated at iii. As shown, the vertical ring of the reference iii positions the rotor of a selsyn device li fed by a suitable source of alternating current electrical energy generally indicated at i2. The stator of device l i is xed to the aircraft employing the improved automatic pilot. The output of device il is fed to a second selsyn device i4 by way oi leads l5, l5 and i7. The rotor of device it, as shown, is positioned by motive means or electrical motor 2i) by Way of shaft 2i, reduction gearing 22 and shaft 23. The combined devices Il and lli provide a pair of interconnected pickoifs having the rotor part of one xed to and rotatable with the azimuth reference device it and the rotor of the other connected to be operated by the motor 2B, the stators of the pickofls being secured to the craft. The pair of pick-offs or signal generators Si and iii together act as a single pick-o having one part positioned by gyro It and the other part positioned by the motor 20. In other words, the beck-to-back. selsyns ll and i4 constitute a means for providing a signal corresponding to relative movement between the directional reference it and the follow-up motor 2l] while the turn control of the present invention is in operation. The pair of piclooifs ii and ifi provide a signal upon relative displacement of Jrhe respective rotor parts thereof from a position of agreement or null position.

In straight line flight of the craft, the picloofi ii operates in a conventional manner, with rotor of device i4 stationary, to provide a signal at leads Si and 25 which varies in accordance with any deviation of the craft from a predetermined heading. This deviation is corrected by operation of the rudder servomotor of the automatic pilot, generally indicated at Zt, which moves the rudder 2l or the craft to restore it to the desired heading. The signal at leads 2t, 25 is fed the servomotor 25 by way of a conventional type of rudder servo amplifier 23 having a rate section 3Q anda displacement section 3i such as that disclosed in my U. S. Patent 2,415,430 jointly with C. A. Frische and J. R. Wilkerson,

issued February ll., i947, and assigned to the assignee of the present application. As shown, the signal at leads 25 is fed to the rate section 3@ of the ampliiier by way of double pole, double throw switch 32 and leads 33, Se. The input to the displacement section 3l is provided by way of leads S5, 36 and leads 31, 38. The output of amplifier 23 which combines both the rate and displacement signals of the respective sections 3d, 3l operates the rudder servomotor 25 of the automatic pilot under straight line conditions of flight of the craft in a conventional manner.

The automatic pilot, as shown, also includesa conventional type of aileron control for the craft. The ailerons for the craft are indicated at it and the controls for the same include an aileron servomotor di, an aileron servo amplifier t2 having rate and displacement sections 3, dit, respectively, similar to those used in connection with the rudder control of the craft. The signal inputs to sections 33, le are provided by the roll pick-off i5 of conventional form of a vertical reference such as a gyro vertical le fed thereto by way of the respective leads e8, i9 and 5i, 52. A further signal supplied to the aileron amplifier 42 is a roll command signal which is produced by displacing the potentiometer 68 and thereby unbalancing the bridge lll, as will be hereinafter more fully described.

In accordance with the invention, the automatic pilot includes a normally ineffective follow up system providing means for making stabilized turns at the natural rate of turn of the craft for a given bank angle and air speed, the same including an amplifier 53 connected to leads 3l, 38 by way of the normally open switch 55.. With switch 5. in its closed position, i. e. thrown to the right, the amplifier 53 provides an output that energizes motor 2Q to drive or move the rotor of selsyn device lll in accordance with the signal at leads 24, 25. Motor 2i! also drives a generator 55 which feeds back a signal to amplifier 53 by way of winding 55 and leads 57, 53 to make the rotational speed of the motor 2li of the motorgenerator set proportional to the amplitude of the signal at leads 2d, 25.

The follow-up amplifier 53 and motor-generator set cooperate to turn the rotor of selsyn device Hi at such a rate as to keep the signal at leads 24, 25 very nearly zero. The amplifier 53 advantageously has a very high gain so that the motor Eil will operate during turns on appearance of even a very small signal at leads 2li, 25. As shown, the motive means or electric motor 2B of the follow-up system is operatively connected to a y-wheel Sil on shaft 2l which tends to maintain the motor at a, constant speed when the craft is yawing. The follow-up also includes, the interconnected pick-offs comprising selsyn devices l! and id and the azimuth reference ill. The system is preferably overdaniped by the signal provided by the winding 56 of the generator 55.

The improved automatic pilot includes means for causing the craft to bank and turn. Such means is provided by a turn knob El which through shaft e2 positions a cam piece 53 to move a cam follower 8d on rod 55 to simultaneously move switch 32 to its dotted line position in Fig. l and close switch 565 to render the follow-up system effective. Spring 66 normally positions the rod 65 so that the respective switches 32 and 54 are located in the full line positions thereof shown in Fig. 1. The turn knob 6l may be provided with a scale el fixed to the craft graduated in terms of rate of turn for a given air speed to the right and left of a zero position. When moved from Zero position, the turn knob 5l also moves the arm 68 of one of a pair of potentiometers to unbalance an electrical bridge l and feed an input to the amplifier 2 by way of leads ll, l2. Until the bank signal from the bridge 'l5 is balanced by an equal and opposite signal from roll pick-off e5, the craft rolls about its fore and aft axis. When the balanced condition is reached the craft is at a predetermined bank angle for the turn. In accordance with the invention, as soon as the craft rolls and pick-off i5 produces an output signal, a portion of the signal is fed to the rate section 3d of the rudder servo amplifier 28 by way of leads T3, M switch 3.2 and leads 33, 3Q. In turns, the signal from the pick-ofi l5 at leads 2e, 25 to the rate section 3G of the rudder servo amplier is by-passed by the switch 32 which is then in its dotted line position in Fig. l. This arrangement provides a means for providing a signal which varies in accordance with the rate of roll of the craft. The roll rate signal from the section 3B is then fed to the rudder servomotor 25 of the automatic pilot to cause the craft to turn about its vertical axis as the same moves ..0 the desired banking angle. When the signal at 5.5 is equal and opposite to that of the bridge le, the output at the rate section 39 of the rudder servo amplifier 28 becomes Zero. A suitable position repeatback may be employed in a conventional manner to insure that the rudder will be returned to its centralized or streanili le position when thev output of the amplier 2% is zero. Thus, the turn is initiated and will be maintained by the inherent directional stability of the craft vuntil the turn knob 6l is returned to its detent position at which time the reverse of the above sequence of operation will occur.

At this time, the signal appearing at leads 2li, 25 from the interconnected pick-offs provided by selsyn devices li and lt is fed by way of leads 35, 36 to the amplifier 5S to drive the motive means 2t or" the motor-generator set and is also fed to section 3l by way of leads 3l, 3E. However, the motor 2d turns the rotor of device ift at a rate corresponding to the natural rate of turn of the craft and the signal at leads 2li, 25 is reduced to substantially zero. rThe flywheel 5S in the system tends to maintain the speed of motor 25 constant and corresponding to the craits natural rate of turn.

Sufcient inertia is given to the follow-up motor 2! by the addition of flywheel dil to effect short period stability. Thus, should an outside disturbance or gust occur during the turn causing the rate of turn to change relatively rapidly, the follow-up including motor 26 will either lead or lag the craft suiiiciently to cause a relatively large signal to appear across leads 24, 25 to section 3l of the rudder amplier 28. This signal moves the rudder before the speed or motor 2) can change materially to restore the crafts turn rate to its natural rate of turn. The automatic pilot is accordingly effective during turns to correct the rate of turn of the craft when such rate departs from the natural turn rate.

If the craft departs from its natural turn rate very slowly, very little correcting signal would be fed to amplifier 3| for the follow-up would then have sufficient time to change its speed thus keeping the signal at 2d, 25 substantially zero. If the craft departs from its natural turn rate rapidly, a large signal is fed to amplier 3l as the inertia in the system provided by ilywheel ell prevents the follow-up motor 26 from changing its speed accordingly as it does not have sufficient time t0 do so. It will be understood, that the established speed of operation of motor 2U corresponds to the natural turn rate of the craft. The banked turn of the craft is properly coordinated for any air speed since in all cases the follow-up system will eventually reduce the signal at 2li, 25 to substantially zero for a steady turn. The time for motor 2c of the follow-up system to change its speed is made longer than the time for the craft to return to its natural rate of turn. Motor 2Q of the folloW-up system provides a means for measuring the natural turn rate of the craft. The flywheel 5G for motor 2B provides a means for resisting change in the measurement provided by the motor.

If, during the turn, a gust or other disturbance should occur which increases or decreases the bank angle set in by contro knob 5l, a signal varying in accordance with the rate of change of bank angle Will be supplied to the rudder servomotor to quickly apply rudder to counteract any tendency of the craft to turn as a result of the changed bank angle.

The automatic pilot may also include an off-on switch 'I5 which is eifeotive when the device is in an off posi-tion to energize motor 2c by an input from amplifier 53 by way of leads l5, l1 to zeroize the signal at leads 2Q, 25 and properly position the rotor of device I4 so that the automatic pilot may be turned on by the operator at any time.

in the modification of the invention shown in Fie. 2, the rate of roll signal providing means for the improved automatic pilot is provided by a gyroscope lil for measuring the rate of movement of the craft about its roll or fore and aft axis. The rate gyroscope 'I8 is operatively conn nected to a pick-off in the form of an electrical bridge 'i9 Whose movable arm 3B is operated by the gyroscope. In this form of the invention, the bridge network 'IS will feed a signal which varies in accordance with the rate of roll of the craft directly to the displacement section 3i oi rudder servo amplifier 28 by Way of leads SI and 82, bypassing the rate section 36 of the rudder' servo amplifier 28. As above, the signal corresponding to the roll rate of the craft will cause the yatv control surface to be displaced in an amount determined by the rate of roll of the craft. Therefore, upon commanding a roll or rate of turn, the craft will bank about its foreuand-aft axis and simultaneously yaW about its vertical axis. When the bank angle of the craft is established, the output of the bridge '15 becomes zero and, as above, the rudder is returned` to its streamline position and the craft will continue to turn due to its inherent directional stability at a rate determined by the bank angle.

Since many changes could be made in the above construction and many apparently Widely dinerent embodiments of this invention could be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. In an automatic pilot for aircraft capable of turning and approximately retaining a constant rate of turn at a constant banking angle, means for causing the craft to bank and turn at its natural rate of turn, a rudder servcniotor, and means for operating said rudder servomotor to correct the rate of turn when such rate departs from the natural rate of turn of the craft comprising a follow up system including an azimuth reference, a pair of interconnected pick-offs having stator and rotor parts providing a signal upon relative displacement of the respective rotor parts from positional agreement, the rotor part of one of the pickeoffs being fixed to said azimuth reference, motive means responsive to the signal of said pick-offs operatively connected to move the rotor part of the other of said pick-oI2 at a rate corresponding to the natural rate of t lrn of the craft, inertia means for said motive means whereby the time for the motive means to change 1ts speed is made longer than the time required for the craft to return to its natural rate of turn after departure therefrom, and means operatively connecting said pair of pick-offs and the rudder servomotor.

2. An automatic pilot as claimed in claim l, in which said pair of pick-offs provides an electrical signal, said motive means is an electric motor driven by the signal of said pair of pick-offs, and said inertia means is a flywheel driven by said motor tending to maintain the motor at a constant speed during turns.

3. An automatic pilot turn control for dirigible craft including a follow up system having motive means, means for operating said motive means during turns at a speed corresponding to the natural rate of turn of the craft, inertia means tending to maintain the speed of the motive means constant, means for measuring departure of the craft fron-i its natural rate of turn responsive to said operating means, and means operated by said measuring means for restoring the craft to its natural rate of turn.

e. An automatic pilot turn control for dirigible craft including a follow up system having motive means operable during turns at a speed corresponding to the natural rate of turn of the craft, an inertial device driven by said "notive means of such character that the time required for the motive means to change its speed is longer than the time required for the craft to return to its natural rate of turn after departure therefrom, and means operated by said nic-tive means for restoring the craft to its natural turn rate.

5. An aircraft automatic pilot having a normally ineffective follow up system including an azimuth reference, a pair or interconnected pickoifs having stator and rotor parts providing a signal upon relative displacement of the respective rotor parts from positional agreement, the rotor part of one of the pick-offs being fixed to said azimuth reference, motive means responsive to the signal of said pick-offs for moving the rotor part of the other of said piclcoffs at a speed corresponding to the natural of turn of the craft, inertia means for maintaining active means at a constant speed, means for causing the craft to bank to a fixed angle and turn at a rate corresponding to its natural rate of turn, means operated by said turn ca ng means for rendern ing said follow up system effective, and means opn erated by said pick off when the craft departs from its natural rate of turn for returning the craft toits natural rate of turn.

6. An aircraft automatic pilot having a rudder servomotor, an aileron servomotor, manually settable means for operating said aileron servcmotor to cause the craft to roll to a predetermined bank angle, means for providing a signal in accordance with the rate of roll of the craft, means for operating said rudder servomotor by the signal of said rate of roll signal providing means to cause the craft to yaw; and second rudder servomotor operating means operable to maintain the craft at its natural rate of turn for the prede-- termined bank angle, comprising a follow up system including an azimuth reference, a pair of interconnected pick-offs having stator and rotor parts providing a signal upon relative displacement of the respective rotor parts from positional agreement, the rotor part of one of the pick-offs being fixed to the azimuth reference, motive means responsive to the signal of said pick-offs for moving the rotor part of the other of the pick-offs, and inertia means for resisting change in the speed of operation of said motive means.

'7. An automatic pilot as claimed in claim 6, in which said rate of roll signal providing means includes a gyroscope measuring the rate of movement of the craft about its roll axis and a pick off operatively connected thereto.

8. An automatic pilot as claimed in claim 6, in which said rate of roll signal providing means includes a gyroscope providing a reference for the craft about its roll axis, a signal pick off operatively connected thereto, and means for providing a signal in accordance with the rate of change of the signal of the pick olf connected to the gyroscope.

9. An aircraft automatic pilot turn control, means for banking said craft to a predetermined bank angle whereby to cause said craft to turn at a rate corresponding to the rate of turn established by said bank angle, reference means including a signal generating means for providing a signal corresponding to the reference rate of turn cf said craft in space as established by said bank angle, a follow-up servo loop comprising a servomotor responsive to said reference signal and adapted to be driven at a speed corresponding to the reference rate of turn of said craft, inertia means coupled with said follow-up servomotor tending to maintain the speed thereof in correspondence with the then pre-existing rate of turn upon transient changes in the rate of turn as reected by said reference means, a second servo loop comprising a servomotor responsive to said rate of turn reference signal and adapted to control the rate of turn of said craft, the response of said follow-up servo loop to said reference signal being relatively slow as compared with the response of said second servo loop to said reference signal whereby short-period changes in the rate of turn of said craft will be corrected by said second servo loop before an appreciable change in speed of said follow-up servo loop can occur.

10. An aircraft automatic pilot turn control, a rudder servomotor and control means therefor, an aileron servomotor, settable means connected to operate said aileron servomotor whereby to cause the craft to roll to a predetermined bank angle, means for providing a signal which varies in accordance with the rate of roll of said craft, and means connected to be operated simultaneously with said settable means for rendering said rate of roll signal effective to control said rudder servomotor control means.

ll. In an aircraft automatic pilot turn control, a rudder servomotor and control means therefor, turn control means operable to cause said craft to roll to a predetermined bank angle, means for providing a signal which varies in accordance with the rate of roll of the craft, and means simultaneously operable with said turn control means for rendering said rate of roll signal eective to control said-rudder servomotor control means.

12. In an aircraft automatic pilot, a rudder and rudder servomotor, control means for said servomotor, a roll attitude reference device for providing a signal which varies in accordance with the displacement of said craft in roll from a predetermined roll attitude, means for differentiating said displacement signal, and means for supplying the resultant signal to said rudder servomotor control means whereby to displace said rudder in an amount corresponding to the rate of roll of the craft.

13. In an aircraft automatic pilot, a rudder and rudder servomotor, control means for said servomotor, a rate of roll gyro including signal generating means for providing a signal which varies in accordance with the rate of roll of said craft, and means for supplying said rate of roll signal to said rudder servomotor control means whereby to displace said rudder in an amount corresponding to the rate of roll of the aircraft.

14. in an aircraft automatic pilot turn control, a rudder servomotor and control means therefor, an aileron servomotor and control means therefor, a yaw reference for supplying yaw control signals to said rudder servomotor control means, turn command means for supplying roll command signals to said aileron servomotor control means whereby to cause said craft to roll to a predetermined bank angle, means for providing a signal which varies in accordance with the rate of roll of said craft, and means actuated by said turn command means for rendering said yaw reference ineffective and for supplying said rate of roll signal to said yaw servomotor control means during command turns whereby to control the rudder during said command turns in an amount dependent upon the rate of roll of said craft.

l5. An aircraft automatic pilot turn control including roll and yaw control surfaces, roll and yaw servomotors for actuating said surfaces, roll and yaw servomotor control means, and a roll reference device, a turn command control comprising settable means coupled with said roll reference for providing a roll displacement signal, means for supplying said roll displacement signal to said roll servomotor control means whereby to roll said craft to a predetermined bank angle through said roll control surfaces, means for providing a signal which varies in accordance with the rate of roll of said craft, and means for supplying said roll rate signal to said yaw servomotor control means whereby to displace said yaw control surface in an amount dependent upon the rate of roll of said craft.

16. An aircraft automatic pilot turn control including roll and yaw control surfaces, roll and yaw servomotors for actuating said surfaces, means for controlling said servomotors, and a roll reference device, a turn command control comprising settable means coupled with said roll reference for providing a roll displacement signal, means for supplying said roll displacement signal to said roll servomotor control means whereby to roll said craft to a predetermined bank angle through said roll control surfaces, means for providing a signal which varies in accordance with the rate of roll of said craft, and means actuated by said settable means for supplying said roll rate signal to said yaw servomotor control means whereby to displace said yaw control surface in an amount dependent upon the rate of roll of said craft.

17. An aircraft automatic pilot turn control including roll and yaw servomotors and control means for operating said servomotors, a roll reference device, a turn command control cornprising settable means coupled with said roll reference for providing a roll displacement signal, means for supplying said roll displacement signai to said roll servomotor control means whereby to roll said craft to a predetermined bank angle, means actuated by said settable means for supplying said roll displacement signal to said yaw servomotor control means, said l yaw servomotor control means including means for deriving from said roll displacement signal a derivative signal varying in accordance with the rate of change of said roll displacement signal and said yaw servomotor being controlled by said derivative signal only.

18. An aircraft automatic pilot turn control including roll and yaW control surfaces, roll and yaw servomotors for actuating said surfaces, control means for said servomotors, and a roll reference device, a turn command control means coupled with said roll reference device for providing a roll displacement signal, means for supplying said roll displacement signal to said roll servomotor control means whereby to roll said craft to a predetermined bank angle through said roll control surfaces, a rate of roll gyroscope including means for providing a signal which varies in accordance with the rate of roll of said craft, and means actuated by said settable means for supplying said roll rate signal to said yaw servomotor control means.

19. An aircraft automatic pilot turn control including roll and yaw servomotors, control means for said servomotors, a roll reference, turn command means coupled with said roll reference for supplying a signal to said roll servomotoi` whereby to roll said craft to a predetermined bank angle, means for providing a signal which varies in accordance with the rate of roll of said craft, nrst switch means actuated by said turn command means for supplying said rate of roll signal to said yaw servomotor control means whereby to cause said craft to turn simul taneously with rolling thereof, a directional reference for providing a signal corresponding to the displacement of said craft from a predetermined yaw attitude, motive means coupled with said directional reference, and second switch .means actuated simultaneously with said first switch means for supplying said yaw dispiacement signal to said motive means whereby to eectively rotate said directional reference at a rate corresponding to the rate of turn of said raft. i

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